U.S. patent number 5,246,027 [Application Number 07/884,645] was granted by the patent office on 1993-09-21 for cargo tank relief valve with sudden surge protection.
This patent grant is currently assigned to Clay and Bailey Manufacturing Company. Invention is credited to Carrol V. Morris.
United States Patent |
5,246,027 |
Morris |
September 21, 1993 |
Cargo tank relief valve with sudden surge protection
Abstract
The relief valve assembly has a spring-loaded poppet valve that
vents the interior of a transport tanker to the atmosphere when
gaseous pressure within the tank exceeds a predetermined limit.
Sudden surge protection from a pressure spike created by liquid
within the tank during the instant that the tank strikes the ground
during accidental roll over is provided to keep the poppet valve
closed during the surge condition. A reaction piston having one
face that counteracts the face of the poppet valve is exposed to
pressure within the tank simultaneously with the poppet valve, but
the counteracting effect of that surface is normally overcome by a
neutralizing chamber on the opposite side of the reaction piston
which is likewise exposed to the interior of the tank. While
gaseous pressure can reach all working surfaces of the valve
essentially at the same time during gradual, progressive pressure
buildup, in a sudden surge situation the liquid is restricted by
port means from instantaneously entering the neutralizing chamber
so that the reaction piston instead holds the poppet closed at this
time. Once the initial liquid surge has passed, pressure within the
tank can gradually enter the neutralizing chamber to allow the
poppet valve to open in the usual manner if pressure exceeds the
predetermined limit.
Inventors: |
Morris; Carrol V. (Cosby,
MO) |
Assignee: |
Clay and Bailey Manufacturing
Company (Kansas City, MO)
|
Family
ID: |
25385048 |
Appl.
No.: |
07/884,645 |
Filed: |
May 15, 1992 |
Current U.S.
Class: |
137/43; 137/494;
220/203.29 |
Current CPC
Class: |
B65D
90/34 (20130101); F16K 17/04 (20130101); F16K
17/36 (20130101); Y10T 137/7781 (20150401); Y10T
137/0874 (20150401) |
Current International
Class: |
B65D
90/22 (20060101); B65D 90/34 (20060101); F16K
17/04 (20060101); F16K 17/36 (20060101); F16K
017/04 () |
Field of
Search: |
;137/38,39,43,494
;220/203 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Nilson; Robert G.
Attorney, Agent or Firm: Hovey, Williams, Timmons &
Collins
Claims
I claim:
1. In a pressure relief valve assembly for volatile liquids having
a discharge outlet, discharge passage means communicating with said
outlet, a valve shiftable by pressure buildup in said passage means
from a closed position closing the outlet to an open position
opening the outlet, and means for yieldably biasing the valve
toward said closed position to maintain the valve normally closed,
improved sudden surge protection apparatus for the assembly
comprising:
a reaction piston movable with the valve and having a working
surface exposed to said passage means simultaneously with the valve
in a disposition for counteracting the tendency of a sudden surge
of liquid to open the valve;
a neutralizing surface operably associated with said reaction
piston for exposure to gaseous pressure buildup simultaneously with
the working surface of the piston in a disposition for
counteracting the effect of the working surface of the reaction
piston during such gaseous pressure buildup; and
restricted access means communicating said neutralizing surface
with the exterior of the assembly in a manner to delay access to
the neutralizing surface by a sudden liquid surge while permitting
said simultaneous exposure of the working surface and the
neutralizing surface to gradual gaseous pressure buildup whereby to
protect the valve against opening during a sudden liquid surge,
said valve having an operating surface operably associated
therewith which has a fixed amount of surface area in communication
with said passage means for causing the valve to shift to said open
position when pressure buildup against the operating surface
exceeds a certain predetermined level,
said neutralizing surface of the reaction piston having the same
amount of exposed surface area in both the open and closed
positions of the valve.
2. In a pressure relief valve assembly as set forth in claim 1,
said neutralizing surface comprising part of said piston.
3. In a pressure relief valve assembly as set forth in claim 2,
said piston having a pair of oppositely directed faces with respect
to the path of travel of the piston during movement between its
open and closed positions,
said surfaces being on opposite ones of said faces.
4. In a pressure relief valve assembly as set forth in claim 1,
said restricted access means including port means dimensioned to
limit the volume of surging liquid that can reach said neutralizing
surface of the reaction piston within a predetermined amount of
time.
5. In a pressure relief valve assembly as set forth in claim 1,
said assembly further including a hollow body provided with an
internal bore which has said outlet at one end thereof and an outer
wall having lateral inlets therein for communicating the bore with
the ambient pressure of the interior of the tank,
said valve having an axially extending stem secured thereto,
said reaction piston being secured to the stem in spaced relation
to the valve for defining a working pressure chamber therebetween
which is in continuous communication with the interior of the tank
via said lateral inlets,
said working pressure chamber comprising said passage means, and
said working surface of the piston comprising a working face of the
piston exposed to the working pressure chamber,
said body including an inner end wall remote from said outlet,
defining an inner end of the bore, and defining at least a portion
of said restricted access means,
said piston cooperating with the end wall to define a neutralizing
pressure chamber therebetween which is in constant communication
with the interior of the tank via said restricted access means,
said neutralizing surface of the piston comprising a neutralizing
face of the piston directed oppositely from said working face and
exposed to the neutralizing chamber.
6. In a pressure relief valve assembly for volatile liquids having
a discharge outlet, discharge passage means communicating with said
outlet, a valve shiftable by pressure buildup in said passage means
from a closed position closing the outlet to an open position
opening the outlet, and means for yieldably biasing the valve
toward said closed position to maintain the valve normally closed,
improved sudden surge protection apparatus for the assembly
comprising:
a reaction piston movable with the valve and having a working
surface exposed to said passage means simultaneously with the valve
in a disposition for counteracting the tendency of a sudden surge
of liquid to open the valve;
a neutralizing surface operably associated with said reaction
piston for exposure to gaseous pressure buildup simultaneously with
the working surface of the piston in a disposition for
counteracting the effect of the working surface of the reaction
piston during such gaseous pressure buildup; and
restricted access means communicating said neutralizing surface
with the exterior of the assembly in a manner to delay access to
the neutralizing surface by a sudden liquid surge while permitting
said simultaneous exposure of the working surface and the
neutralizing surface to gradual gaseous pressure buildup whereby to
protect the valve against opening during a sudden liquid surge,
said body further including a generally cylindrical spring housing
projecting outwardly from said end wall,
said stem projecting beyond said reaction piston and into said
housing,
said yieldable biasing means including coil spring means contained
within said housing and coupled with said stem in a manner to
yieldably urge to the valve toward its closed position,
said assembly further including a hollow body provided with an
internal bore which has said outlet at one end thereof and an outer
wall having lateral inlets therein for communicating the bore with
the ambient pressure of the interior of the tank,
said valve having an axially extending stem secured thereto,
said reaction piston being secured to the stem in spaced relation
to the valve for defining a working pressure chamber therebetween
which is in continuous communication with the interior of the tank
via said lateral inlets,
said working pressure chamber comprising said passage means, and
said working surface of the piston comprising a working face of the
piston exposed to the working pressure chamber,
said body including an inner end wall remote from said outlet,
defining an inner end of the bore, and defining at least a portion
of said restricted access means,
said piston cooperating with the end wall to define a neutralizing
pressure chamber therebetween which is in constant communication
with the interior of the tank via said restricted access means,
said neutralizing surface of the piston comprising a neutralizing
face of the piston directed oppositely from said working face and
exposed to the neutralizing chamber,
said body further including a generally cylindrical spring housing
projecting outwardly from said end wall,
said stem projecting beyond said reaction piston and into said
housing,
said yieldable biasing means including coil spring means contained
within said housing and coupled with said stem in a manner to
yieldably urge to the valve toward its closed position.
7. In a pressure relief valve assembly as set forth in claim 6,
said spring housing having port means therein comprising at least a
portion of said restricted access means,
said housing including a sidewall and said port means including a
port in said sidewall.
8. In a pressure relief valve assembly as set forth in claim 7,
said spring housing including a transverse end wall having an
opening that comprises a portion of said port means,
said stem being disposed to restrict flow into the housing through
the opening when the valve is closed and to diminish the amount of
restriction through the opening when the valve is opened.
9. In a pressure relief valve assembly as set forth in claim 6,
said coil spring means including a pair of concentrically disposed
coil compression springs operably coupled with one another in a
series relationship to reduce the effective spring rate of the coil
spring means.
10. In a manhole cover assembly for attachment to the wall of a
storage tank having an manhole therein, the improvement
comprising:
a cover plate adapted to span said manhole when the assembly is
attached to the tank;
means for releasably securing the plate on the tank in spanning
relationship to said manhole;
a fill opening in said plate;
lid hingedly secured to said plate for swinging movement between
positions opening and closing said fill opening;
releasable latch means on the lid and the plate for releasably
securing the lid in its position closing the fill opening;
an aperture in said lid disposed for alignment with the fill
opening when the lid is in its position closing the fill opening;
and
a pressure relief valve assembly secured to said lid and received
within said aperture for venting the interior of the tank to the
atmosphere in the event of a gaseous pressure buildup within the
tank beyond a certain predetermined level,
said valve assembly including:
a discharge outlet;
discharge passage means communicating with said outlet;
a valve shiftable by gaseous pressure buildup in said passage means
from a closed position closing the outlet to an open position
opening the outlet;
means for yieldably biasing the valve toward said closed position
to maintain the valve normally closed;
a reaction piston movable with the valve and having a working
surface exposed to said passage means simultaneously with the valve
in a disposition for counteracting the tendency of a sudden surge
of liquid to open the valve;
a neutralizing surface operably associated with said reaction
piston for exposure to gaseous pressure buildup simultaneously with
the working surface of the piston in a disposition for
counteracting the effect of the working surface of the reaction
piston during such gaseous pressure buildup; and
restricted access means communicating said neutralizing surface
with the exterior of the assembly in a manner to delay access to
the neutralizing surface by a sudden liquid surge while permitting
said simultaneously exposure of the working surface and the
neutralizing surface to gradual gaseous pressure buildup whereby to
protect the valve against opening during a sudden liquid surge.
11. In a manhole cover assembly as set forth in claim 10,
said neutralizing surface comprising part of said piston.
12. In a manhole cover assembly as set forth in claim 11,
said piston having a pair of oppositely directed faces with respect
to the path of travel of the piston during movement between its
open and closed positions,
said surfaces being on opposite ones of said faces.
13. In a manhole cover assembly as set forth in claim 10,
said restricted access means including port means dimensioned to
limit the volume of surging liquid that can reach said neutralizing
surface of the reaction piston within a predetermined amount of
time.
14. In a manhole cover assembly as set forth in claim 10,
said assembly further including a hollow body provided with an
internal bore which has said outlet at one end thereof and an outer
wall having lateral inlets therein for communicating the bore with
the ambient pressure of the interior of the tank,
said valve having an axially extending stem secured thereto,
said reaction piston being secured to the stem in spaced relation
to the valve for defining a working pressure chamber therebetween
which is in continuous communication with the interior of the tank
via said lateral inlets,
said working pressure chamber comprising said passage means, and
said working surface of the piston comprising a working face of the
piston exposed to the working pressure chamber,
said body including an inner end wall remote from said outlet,
defining an inner end of the bore, and defining at least a portion
of said restricted access means,
said piston cooperating with the end wall to define a neutralizing
pressure chamber therebetween which is in constant communication
with the interior of the tank via said restricted access means,
said neutralizing surface of the piston comprising a neutralizing
face of the piston directed oppositely from said working face and
exposed to the neutralizing chamber.
15. In a manhole cover assembly as set forth in claim 14,
said body further including a generally cylindrical spring housing
projecting outwardly from said end wall,
said stem projecting beyond said reaction piston and into said
housing,
said yieldable biasing means including coil spring means contained
within said housing and coupled with said stem in a manner to
yieldably urge to the valve toward its closed position.
16. In a manhole cover assembly as set forth in claim 15,
said spring housing having port means therein comprising at least a
portion of said restricted access means,
said housing including a sidewall and said port means including a
port in said sidewall.
17. In a manhole cover assembly as set forth in claim 16,
said spring housing including a transverse end wall having an
opening that comprises a portion of said port means,
said stem being disposed to restrict flow into the housing through
the opening when the valve is closed and to diminish the amount of
restriction through the opening when the valve is opened.
18. In a manhole cover assembly as set forth in claim 15,
said coil spring means including a pair of concentrically disposed
coil compression springs operably coupled with one another in a
series relationship to reduce the effective spring rate of the coil
spring means.
19. In a cargo tank for volatile liquids, the improvement
comprising:
a tank wall;
an aperture in said wall; and
a pressure relief valve assembly mounted on said wall and received
within said aperture for venting the interior of the tank to the
atmosphere in the event of a gaseous pressure buildup within the
tank beyond a certain predetermined level,
said valve assembly including:
a discharge outlet;
discharge passage means communicating with said outlet;
a valve shiftable by gaseous pressure buildup in said passage means
from a closed position closing the outlet to an open position
opening the outlet;
means for yieldably biasing the valve toward said closed position
to maintain the valve normally closed;
a reaction piston movable with the valve and having a working
surface exposed to said passage means simultaneously with the valve
in a disposition for counteracting the tendency of a sudden surge
of liquid to open the valve;
a neutralizing surface operably associated with said reaction
piston for exposure to gaseous pressure buildup simultaneously with
the working surface of the piston in a disposition for
counteracting the effect of the working surface of the reaction
piston during such gaseous pressure buildup; and
restricted access means communicating said neutralizing surface
with the exterior of the assembly in a manner to delay access to
the neutralizing surface by a sudden liquid surge while permitting
said simultaneously exposure of the working surface and the
neutralizing surface to gradual gaseous pressure buildup whereby to
protect the valve against opening during a sudden liquid surge.
20. In a cargo tank as set forth in claim 19,
said neutralizing surface comprising part of said piston.
21. In a cargo tank as set forth in claim 20,
said piston having a pair of oppositely directed faces with respect
to the path of travel of the piston during movement between its
open and closed positions,
said surfaces being on opposite ones of said faces.
22. In a cargo tank as set forth in claim 19,
said restricted access means including port means dimensioned to
limit the volume of surging liquid that can reach said neutralizing
surface of the reaction piston within a predetermined amount of
time.
23. In a cargo tank as set forth in claim 19,
said assembly further including a hollow body provided with an
internal bore which has said outlet at one end thereof and an outer
wall having lateral inlets therein for communicating the bore with
the ambient pressure of the interior of the tank,
said valve having an axially extending stem secured thereto,
said reaction piston being secured to the stem in spaced relation
to the valve for defining a working pressure chamber therebetween
which is in continuous communication with the interior of the tank
via said lateral inlets,
said working pressure chamber comprising said passage means, and
said working surface of the piston comprising a working face of the
piston exposed to the working pressure chamber,
said body including an inner end wall remote from said outlet,
defining an inner end of the bore, and defining at least a portion
of said restricted access means,
said piston cooperating with the end wall to define a neutralizing
pressure chamber therebetween which is in constant communication
with the interior of the tank via said restricted access means,
said neutralizing surface of the piston comprising a neutralizing
face of the piston directed oppositely from said working face and
exposed to the neutralizing chamber.
24. In a cargo tank as set forth in claim 23,
said body further including a generally cylindrical spring housing
projecting outwardly from said end wall,
said stem projecting beyond said reaction piston and into said
housing,
said yieldable biasing means including coil spring means contained
within said housing and coupled with said stem in a manner to
yieldably urge to the valve toward its closed position.
25. In a cargo tank as set forth in claim 24,
said spring housing having port means therein comprising at least a
portion of said restricted access means,
said housing including a sidewall and said port means including a
port in said sidewall.
26. In a cargo tank as set forth in claim 25,
said spring housing including a transverse end wall having an
opening that comprises a portion of said port means,
said stem being disposed to restrict flow into the housing through
the opening when the valve is closed and to diminish the amount of
restriction through the opening when the valve is opened.
27. In a cargo tank as set forth in claim 24,
said coil spring means including a pair of concentrically disposed
coil compression springs operably coupled with one another in a
series relationship to reduce the effective spring rate of the coil
spring means.
Description
TECHNICAL FIELD
This invention relates to pressure relief valves utilized in
connection with over-the-road tanker trucks and the like and, more
particularly, to a relief valve which permits venting to the
atmosphere when the interior of the tank exceeds a predetermined
pressure level yet which has built-in sudden surge protection to at
least substantially prevent opening of the relief valve in response
to a sudden liquid pressure surge during accidental roll-over of
the tanker.
BACKGROUND ART
Cargo tanks which handle volatile liquids must be provided with
relief valves to permit the interior of the tank to be vented to
the atmosphere if the pressure inside of the tank increases to an
excessive level due to heat exposure, for example. However, in the
event the tank is rolled over during a vehicular accident, it is
desirable that the relief valve not be allowed to open during the
instant that a high pressure, sudden liquid surge arises within the
tank as it strikes the ground. If the valve were allowed to open at
that time, the surging liquid could spray and spew the volatile
contents over a wide area in the vicinity of the rollover and
present a very dangerous situation. On the other hand, once the
sudden liquid surge has passed, it is important that the relief
valve then be capable of performing its venting function so that
the pressure within the tank can be gradually released if it
exceeds the relief pressure for any prolonged period of time.
SUMMARY OF THE PRESENT INVENTION
Accordingly, one important object of the present invention is to
provide a cargo tank relief valve which is capable of venting the
interior of the tank to the atmosphere when inside pressure exceeds
a certain predetermined level, yet which is also capable of
remaining at least substantially fully closed during the instant
that a sudden liquid pressure surge is encountered within the tank
during rollover. As an extension to this objective, it is also an
important aspect of the invention to provide for opening of the
relief valve even when the tank is in the rollover condition once
the sudden surge has passed and if the continuing pressure exerted
by the contents then exceeds the preset relief pressure of the
valve.
Another important object of the present invention is to make the
sudden surge protection portion of the relief valve directly
responsive to pressure levels within the tank, rather than
indirectly responsive through the use of pilot-operated,
intermediate moving components and springs such as sometimes
utilized in prior art devices. In this respect, it is also
important that the sudden surge portion of the valve be
pressure-responsive rather than gravity actuated in contrast to
certain prior art arrangements so that reliability is
increased.
In carrying out the foregoing and other objects, the present
invention contemplates a relief valve having a spring loaded poppet
that is designed to move against the contrary urging of a biasing
spring when pressure within the tank exceeds a predetermined level
so that the poppet is opened to allow venting of the pressurized
vapors to the atmosphere. In order to prevent the poppet valve from
responding in the same manner to a sudden pressure spike or surge
from the contained liquid during rollover, the poppet valve is
provided with a special reaction piston having a working surface
that faces in the opposite direction from the corresponding surface
of the poppet valve and which is exposed to either the pressurized
gaseous vapors or sudden liquid surge at the same time as the
poppet valve. Thus, the working surface of the reaction piston
tends to counteract the force tending to open the poppet valve.
However, the underside of the reaction piston is also exposed to
the pressurized gaseous vapors in the tank at the same time as the
other working surfaces so that during normal progressive pressure
build-up within the tank, the two opposite sides of the reaction
piston effectively neutralize one another to produce a net
resultant force of zero in both the valve opening and valve
retaining directions, so that the poppet valve is under the
retaining influence only of the biasing spring at that time. By
making access to the underside of the reaction piston difficult for
liquid in the tank, however, the neutralizing effect of the
underside of the reaction piston is temporarily prevented during a
sudden liquid surge so that the top working surface of the reaction
piston is effective in keeping the poppet valve closed at this
time. Once the pressurized liquid is successful in gaining access
to the undersigned of the reaction piston so as to neutralize the
force exerted on the top working surface of the piston, the poppet
valve may be opened if the pressure exerted against it exceeds the
predetermined level.
In order to restrict access to the underside of the reaction piston
by the surging liquid in the event of a rollover, a restricted
arrangement of inlet ports is provided in communication with the
underside of the reaction piston. Although gaseous vapor can
progressively find its way into the neutralizing chamber that is
defined beneath the underside of the reaction piston as pressure in
the tank progressively builds up during a normal need-to-vent
situation, instantaneous access to the neutralizing chamber by
surging liquid is prevented by the restricted port arrangement.
Moreover, because of the presence of gas in the neutralizing
chamber just prior to the liquid surge, the liquid which would seek
to enter the neutralizing chamber must first compress the gas in
order to do so, thereby further inhibiting quick access to the
underside of the reaction piston by the surging liquid.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary, top plan view of a cargo tank having a
relief valve in accordance with the present invention attached to
the manhole cover assembly associated with the tank;
FIG. 2 is a fragmentary, enlarged, vertical cross-section view of
the valve and associated manhole structure taken substantially
along line 2--2 of FIG. 1;
FIG. 3 is an enlarged, fragmentary cross-sectional view of the
means for attaching the manhole cover assembly to the
manhole-defining collar on the cargo tank;
FIG. 4 is a further enlarged, fragmentary vertical cross-sectional
view through the valve assembly itself showing the poppet valve in
its closed position;
FIG. 5 is a fragmentary cross-sectional view of the valve assembly
similar to FIG. 4, but showing the poppet valve in its open
position; and
FIG. 6 is a fragmentary cross-sectional view of the valve assembly
similar to FIGS. 4 and 5 but illustrating the condition of things
during a sudden liquid surge during rollover of the tank.
DETAILED DESCRIPTION
The cargo tank 10 has a top wall 12 that is provided with a manhole
14 defined by a cylindrical collar 16 fixed to the top wall 12. The
upright collar has a rim portion 16a that projects a short distance
above the surface of the top wall 12, while a lower depending
portion 16b of the collar 16 projects downwardly into the interior
18 of the tank 10.
A manhole cover assembly 20 covers the manhole 14 and includes as
its primary component a large circular plate 22 that spans the
manhole 14 and rests on top of the rim 16a. As shown in FIGS. 2 and
3, the plate 22 overhangs the rim 16a and has an annular sealing
gasket 24 that engages the top edge of the rim 16a to make a
liquid-tight seal with the collar 16 at that point.
As illustrated in FIG. 3, the manhole cover assembly 20 is
detachably secured to the collar 16 via a plurality of bolt
assemblies 26, each of which includes a bolt 28 having a lower
threaded end and a nut 30 threadably received on such lower end.
Each nut 30 has an outturned hook portion 30a that catches under
the lowermost edge of the collar 16 as the nut 30 is drawn up onto
the bolt 28, thus securing the manhole cover assembly 20 in
place.
The cover plate 22 has a fill opening 32 defined therein by an
upstanding circular rim 34. The fill opening 32 is sealed by a lid
36 having a hinged connection with the plate 22 at 38 so that the
lid 36 can be swung between the closed position illustrated in FIG.
1 and an open position in which the fill opening 32 is exposed for
access purposes. A releasable latch 40 having components on the
plate 22 and the lid 36 respectively may be utilized to snugly
secure the lid 36 in its closed position.
The lid 36 is of annular configuration, presenting a central
aperture 42 within which is disposed a relief valve assembly 44
constructed in accordance with the present invention. A pair of
diametrically opposed mounting screws 46 pass through the lid 36
for securing the valve assembly 44 to the lid 36 beneath the
latter. It will be noted that the screws 46 are slidably received
within the lid 36 but are fixedly secured to the valve assembly 44
such that the assembly 44 can move yieldably up and down relative
to the lid 36 against the force of six coil springs 48 spaced
around the aperture 42 at 60.degree. intervals. In this way, an
annular sealing gasket 50 on the underside of a flange 52 of the
valve assembly 44 is pressed yieldably against the rim 34 when the
lid 36 is latched down in its closed position of FIG. 1 and FIG.
2.
With particular reference to FIGS. 4 and 5, it will be seen that
the relief valve assembly 44 includes a hollow valve body 54 of
generally cylindrical configuration having the flange 52 adjacent
its upper end. Most of the valve body 54 hangs down into the
interior 18 of the tank, such that only a relatively small, low
profile upper portion projects beyond the rim 34 of the fill
opening 32. The upper end of the valve body 54 is open so as to
define a venting outlet 56 under the control of a poppet valve 58.
The poppet valve 58 is movable between the closed position
illustrated in FIG. 4 and the open position illustrated in FIG. 5,
there being an O-ring gasket 60 around the beveled peripheral edge
of the poppet 58 that seats against the correspondingly beveled
surface of the outlet 56 when poppet valve 58 is closed.
The valve body 54 has a series of lateral inlets 62 formed in a
sidewall 64 thereof (see also FIG. 2) which serve to communicate
the interior 18 of the tank with an elongated, inner bore 66
defined within the valve body 54 by the side wall 64. The bore 66
is subdivided into an upper reaction chamber broadly denoted by the
numeral 68 disposed immediately below the poppet valve 58, and a
lower neutralizing chamber 70 disposed beneath a reaction piston 72
which is vertically reciprocable within the bore 66. The lateral
inlets 62 open into the reaction chamber 68 such that both the
underside of the poppet valve 58 and the top side of the reaction
piston 72 are simultaneously exposed to pressure from the interior
18 of the tank, whether in the form of gaseous pressure or surging
liquid pressure. Thus, the reaction chamber 68 in a sense serves as
a form of passage means which simultaneously communicate both the
poppet valve 58 and the reaction piston 72 with the interior of the
tank via the inlets 62.
The poppet valve 58 has a centrally disposed, axial stem 74 to
which it is securely attached by a nut 76 threaded onto the upper
end of the stem 74. The stem 74 also fixedly carries the reaction
piston 72 at a location spaced below the poppet 58 so that the
reaction piston 72 and the poppet 58 move together during opening
the closing of the poppet 58. A nut 78 on the bottom side of the
piston 72 is threaded onto a central threaded portion of the stem
74 to securely attach the piston 72 into a permanent location on
the stem 74 relative to the poppet 58.
The reaction piston 72 has an upper working surface 80 exposed to
the chamber 68, and a lower neutralizing surface 82 exposed to the
neutralizing chamber 70. The two surfaces 80, 82 have equal
surfaces areas and are configured to produce a central dome-like
hub 84 in the piston as well as a flat, radially outwardly
extending web 86 at the lower margin of the hub 84. The web 86 has
a sealing 0-ring 88 around its outermost periphery that wipes
against the interior surface of the side wall 64 so as to sealingly
separate the chambers 68 and 70 from one another.
The lower end of the bore 66 is closed by a transverse bottom wall
90 having a centrally disposed, elongated, cylindrical spring
housing 92 secured thereto and projecting in opposite upward and
downward directions from the bottom wall 90. The cylindrical spring
housing 92 has an outer annular side wall 94 that defines an
internal, cylindrical spring chamber 96 which is closed at its
bottom end by a generally transversely U-shaped closure 98. The
opposite, upper end of the spring housing 92 has a centrally
disposed clearance hole 100 which telescopically receives an
inverted, elongated spring cup 102 having its own internal spring
chamber 104. An top transverse wall 106 of the spring cup 102 has a
central opening 108 therein which telescopically receives the
lower, reduced diameter half of the stem 74. The lowermost end of
the stem half is threaded so as to receive a nut 110 thereon which
bears against a spring seat 112 encircling the lower half of the
stem 74 just above the nut 110. Consequently, a coil compression
spring 114 is trapped within the spring chamber 104 between the
seat 112 and the top wall 106 to yieldably bias the poppet valve 58
downwardly toward its closed position of FIG. 4.
Assisting the coil spring 114 in this respect is a second, larger
diameter coil compression spring 116 that encircles the spring cup
102 and is trapped between a lower radial flange 118 on the spring
cup 102 and an upper transverse wall 120 of the spring housing 92
within which the clearance hole 100 is defined. The spring rates of
the two springs 114,116 are substantially identical to one another.
As a consequence of this construction, the springs 114,116 are
disposed in a series arrangement such that the effective spring
rate of the resulting combination is cut in half. For a given
amount of total opening force, this causes the poppet 58 to open
twice as far as it otherwise would with only one of the springs 114
or 116 in use.
The closure 98 at the bottom end of the spring housing 92 has a
centrally disposed clearance hole 122 that telescopically receives
the lower threaded end of the stem 74. There is complete clearance
between the walls of the hole 122 and the threads of the stem 74 so
that stem 74 does not wipe against the walls of the hole 122 during
reciprocation of the stem 74.
The sidewall 94 of the spring housing 92 has a port 124
therethrough which communicates the interior of the tank 18 with
the spring chambers 96 and 104, which in turn communicate with the
neutralizing chamber 70 via the clearance hole 100 and the central
opening 108. It will be appreciated that due to the presence of the
clearance hole 122 for stem 74 in the closure 98, pressurized gas
and liquid within the tank interior 18 also have access to the
spring chambers 96 and 104 via the clearance hole 122, although it
is contemplated that access through the clearance hole 122 will be
considerably less than that through the port 124. Consequently, the
clearance hole 122, the port 124, the chambers 96 and 104, and the
hole 100 with the central opening 108 broadly comprise restricted
access means to the neutralizing chamber 70 for pressurized gas and
liquid within the tank interior 18.
Operation
FIGS. 4 and 5 illustrate the valve assembly 44 under normal
operating conditions. As illustrated in FIG. 4, the poppet valve 58
is normally maintained in a closed condition with the O-ring gasket
60 seated firmly against the beveled rim of the venting outlet 56.
This is due to the fact that unless the pressure within the
reaction chamber 68 exceeds a certain predetermined maximum level,
the retaining force generated by the two springs 114 and 116 is
greater than the pressure exerted against the underside of the
poppet valve 58.
When the cargo tank 10 is upright, as illustrated in FIGS. 4 and 5,
the gas vapors within the interior of the tank 18 enter the
reaction chamber 68 via the lateral inlets 62 and also enter the
neutralizing chamber 70 via the port 124 and, to a certain extent,
the clearance hole 122. Thus, the underside of the poppet valve 58,
the top working surface 80 of the reaction piston 72, and the
bottom neutralizing surface 82 of the reaction piston 72 are all
simultaneously exposed to whatever pressure may exist within the
empty space above the volatile liquid 126 within the tank 10.
Inasmuch as the surface areas of the working surface 80 and the
neutralizing surface 82 are identical to one another, there is no
net force created by pressurized vapors in either direction along
the axis of the stem 74 from the reaction piston 72. Thus, the
valve 58 stays closed solely by the action of the biasing springs
114 and 116 at this time.
In the event the pressure level within the space above the liquid
126 progressively increases due to a heat buildup or otherwise,
such buildup will be rather gradual so that it is simultaneously
communicated to the underside of poppet 58, the top working surface
80 of reaction piston 72, and the bottom neutralizing surface 82 of
the reaction piston 72. Consequently, even during the gradual
gaseous pressure buildup, the effect of the reaction piston 72 is
neutralized and the poppet valve 58 remains closed so long as the
force pushing outwardly against the bottom of the poppet 58 does
not exceed the counteracting biasing force of the springs 114 and
116. Once that level is exceeded, however, the poppet valve 58 is
unseated, as illustrated in FIG. 5, allowing the gas to be vented
to the atmosphere. Once sufficient venting has occurred to bring
the opening force below the retaining force of the springs the
valve 58 recloses and the interior of the tank 18 is once again
sealed.
In the event of a roll over, as illustrated in FIG. 6, there will
be a sudden surge by the liquid 116 against parts of the valve
assembly 44 as the tank strikes the ground. As illustrated in FIG.
6, the liquid 126 simultaneously bears against the underside of the
poppet valve 58 and the top working surface 80 of the reaction
piston 72 at that instant. However, due to the fact that access to
the neutralizing chamber 70 is limited by the restricted nature of
the port 124 and the clearance hole 122, the liquid 126 is unable
to reach the underside 82 of the reaction piston 72 simultaneously
with the liquid reaching poppet valve 58 and the top side 80 of
reaction piston 72. Consequently, there is a net increase in the
force retaining the poppet valve 58 closed, such force increase
being derived from the liquid bearing against the top surface 80 of
the reaction piston 72. The force tending to open the poppet 58,
i.e., the liquid bearing against the bottom of the poppet 58, is
thus fully counteracted by liquid against the top surface of
reaction piston 72, and the poppet valve 58 remains closed during
this instant of time.
After a short delay, the liquid gains access to the neutralizing
chamber 70, but by this time the pressure spike caused by the
sudden surge will have dissipated so that while the forces
operating against opposite surfaces 80 and 82 of the reaction
piston 72 cancel out one another, there may no longer be a high
enough pressure exerted against the bottom of the poppet valve 58
to overcome the resistance of springs 114 and 116. Consequently,
the poppet 58 will remain closed. However, if the pressure level
within the tank should rise sufficiently in a progressive manner
such as if the tank 10 is subjected to a fire, the poppet valve 58
will open to vent the contents to the atmosphere instead of
allowing pressure to reach untoward levels within the interior
18.
The duration of a sudden surge in the event of roll over of the
tank is in the neighborhood of 60 milliseconds. Thus, only a very
short delay in opening of the poppet valve 58 is required in order
to provide the necessary sudden surge protection. In the present
invention, such protection is provided without any moving parts or
pilot-operated mechanisms that must first respond to either the
sudden surging pressure or to the effect of gravity in order to
prevent opening of the poppet valve. Instead, in the present
invention, there is a direct hinderance applied against the surging
liquid itself for an instant of time so that the very same medium
attempting to force open the relief valve is itself prevented from
reaching the area necessary to accomplish its purpose.
Consequently, without intermediate, moving parts to fail, the
present invention with its uncomplicated, straight-forward design
is subject to greater reliability and longer life than certain of
the prior art mechanisms.
The total cross-sectional size selected for the inlet port
presented by the port 124 and the clearance hole 122 depends upon
the duration of the surge protection desired and the level of surge
pressure selected to be protected against. It is assumed, of
course, that the greatest restriction to liquid flow into the
neutralizing chamber 70 is found at the port 124 and the clearance
hole 122, rather than at the clearance hole 100 and the central
opening 108. Thus, in all cases, the clearance hole 100 and the
central opening 108 are designed to provide less restriction to
flow than the port 124 and the clearance hole 122.
In order to calculate the cross-sectional size of the port 124 and
the annular space within the hole 122 around the valve stem 74, the
compressible gas formula P.sub.1 V.sub.1 =P.sub.2 V.sub.2 is
utilized, where P.sub.1 equals the starting pressure within the
neutralizing chamber 70, V.sub.1 equals the starting volume of gas
at the starting pressure, P.sub.2 equals the surge pressure to be
kept from entering the neutralizing chamber 70, and V.sub.2 equals
the final volume of the gas trapped within the neutralizing chamber
70 at surge pressure. Since P.sub.1, V.sub.1, and P.sub.2 are known
quantities, the equation can be solved for V.sub.2, and then the
change in volume can be calculated, which will provide a volume
differential equal to the volume of liquid which would need to
enter the neutralizing chamber 70 at the surge pressure before the
pressure on both sides of the reaction piston would be equal and
the effect of the reaction piston 72 would thus be neutralized.
Once the volume of liquid necessary to enter the chamber 70 is
known, the flow rate can be calculated in gallons per minute (GPM)
when a value for duration of time of the surge is applied.
Thereupon, the standard formula for calculating orifice size can be
utilized, i.e., GPM=29.836 CD.sup.2 .sqroot.P, where GPM equals the
flow rate in gallons per minute, C equals a constant for a
sharp-edged orifice (0.62), D equals the diameter in inches of the
orifice being calculated, and P equals the pressure change in
pounds per square inch.
In a preferred embodiment of the present invention, certain values
were established for the cross-sectional inlet port size based upon
an assumed standard which required maintaining the poppet valve 58
closed during a surge pressure of 30 psi lasting for 60
milliseconds. In order to over-design the unit to provide even
increased protection beyond the assumed standard, values were
determined based upon holding a 30 psi surge for 300
milliseconds.
The reduced to practice unit had a poppet valve 58 with a working
underside surface area of 25.36 sq. inches. The upper and lower
surfaces 80 and 82 of the reaction piston were each provided with a
surface area of 30.08 sq. inches. This yielded an area ratio of
1.19 to 1.
With the volume of the neutralizing chamber assumed to be 10.75
cubic inches when the poppet valve 58 was closed, the above noted
formulas yielded a total port or orifice diameter of 0.181
inches.
This construction yielded a relief valve that would open at 31/2
psi above atmospheric pressure, yet would maintain the poppet valve
58 fully closed for a duration far exceeding 60 milliseconds at an
assumed surge pressure of 30 psi.
It will be noted that by virtue of the present design, there is a
low exterior profile presented by the valve assembly 44. Most of
the valve assembly 44 projects down into the interior of the tank
18, rather than up above the exterior thereof. Furthermore, the
interior of the valve assembly is completely shielded from adverse
weather conditions when the poppet 58 is closed, in contrast to
some prior art devices. Consequently, moisture is kept from
entering the valve, collecting in low spots, and freezing up the
parts, rendering the valve inoperable.
Moreover, the design as disclosed herein provides relatively high
capacity venting ability within a given hole size in the lid 36. It
will be noted in this respect that as the poppet valve 58 rises off
the outlet seat 56, there is a complete, uncluttered discharge area
that allows escape of pressurized gas. This is true for the full
360.degree. circumference of the valve 58, thus increasing the
volume of gas per unit time which can be discharged.
The series arrangement of the compression springs 114,116 provides
for an increased amount of poppet valve travel when an opening
force is applied, thus assuring maximum venting capacity.
Consequently, the advantageous effect of a single, long compression
spring with a low spring rate is obtained without the dimensional
disadvantages inherent in such a longer spring.
Additionally, it will be noted that the relief valve of the present
invention may be easily retrofitted onto existing tankers provided
with manholes in their top wall. The present invention may be
embodied in a valve assembly 44 itself, as part of a replacement
fill lid assembly, or as part of an entire manhole cover assembly
to be fastened onto the pre-existing manhole in the tank.
Although preferred forms of the invention have been described
above, it is to be recognized that such disclosure is by way of
illustration only, and should not be utilized in a limiting sense
in interpreting the scope of the present invention. Obvious
modifications to the exemplary embodiments, as hereinabove set
forth, could be readily made by those skilled in the art without
departing from the spirit of the present invention.
The inventor hereby states his intent to rely on the Doctrine of
Equivalents to determine and assess the reasonably fair scope of
his invention as pertains to any apparatus not materially departing
from but outside the literal scope of the invention as set out in
the following claims.
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